I use both
503 CW with winder CW and lenses 120, 80, 40
V series lenses allow for 1/2 stop changes
Mamiya RZ is completely different
I like it very much
AE finder allows 1/6 stop changes !!!
It is heavy and the grip helps a lot
I often use it for a whole day, handheld
but I am happy to release it, from time to time, hanging on the neck brace !
but you get used to it
consider it as "power building"
lenses RZ are tack sharp
too sharp for portraiture I think, hasselblad is better for this, unless you want to see all details ;-)
digital on these camera's ...
MFDB on a Hasselblad, handheld ...troublesome
difficult to focus
RZ is better in this case, but you loose much of the frame 6x7
recently, I went back to film on these beauties.(B/W and Slides)
For digital only, I would suggest to use a system that's designed for digital
Leica S2 or Hasselblad H, Mamiya/Phase 645 digital system